We found this circuit in a publication from the 1970s, but it can still be assembled today by replacing the transistors with more modern types. For UJT we can use 2N2646 and for others we can use 2N2222 or BC548. The circuit is powered by a 12 V supply and the 7474 circuit is of the normal TTL series. A 5 V zener stabilizes the supply voltage of this integrated circuit. The status indication, open, short, or good is given by 3 LEDs that can be of different colors.
